The overall goal of my efforts is to define molecular features of synaptic transmission in the nervous system by studying the operation of NMDA and AMPA receptors. These receptors are neurotransmitter-gated ion channels that convert the presynaptic release of glutamate, the predominant excitatory neurotransmitter in the brain, into a postsynaptic signal. By defining the operation of NMDA and AMPA receptors, we will gain a better understanding of how they control brain function. We will also learn how to modulate their function with greater precision and specificity to help understand, and potentially treat, disease states such as schizophrenia, epilepsy, and the excitotoxicity associated with acute and chronic brain disorders. Our experiments will focus on structural elements of the NMDA and AMPA receptor located to the periphery of those lining the permeation pathway of the ion channel. Recent evidence has indicated that inherited and de novo mutations in these outer or peripheral structures induce developmental disorders and epileptic encephalopathies. These outer structures also contain allosteric sites for drugs of abuse and are targets for newly developed NMDA receptor modulators. Aim 1 will address the impact of the outer structures to the rapid and efficient pore opening that is the hallmark of fast synaptic transmission. For these experiments, we will combine single channel recordings with non-equilibrium conditions to define the energetics of displacement of the outer structures. Aim 2 will address how permeant ions access the central permeation pathway through the outer structures. Aim 3 will address how disease- causing mutations interact at the outer structures to alter NMDA and AMPA receptor function. Here, we will use cysteine cross-linking, fast agonist application, and agonist-free single channel recordings to address how specific elements interact in the outer structures to modulate receptor function. Overall our experiments will delineate how the outer structures contribute to the operation of NMDA and AMPA receptors. This information will aid in defining how disease-causing mutations affect receptor function and in developing specific therapies to target these receptors in nervous system disorders.